Manufacture of fibre-reinforced carbon bodies

ABSTRACT

A MECHANICAL STRENGTH OF A CARBON BODY MADE BY CARBONZIATION OF A PHENOLIC RESIN BODY, WHICH MAY BE SO-CALLED VITREOUS CARBON, IS GREALTLY INCREASED BY EMBODYING THEREIN PRE-STRESSED CARBON FIBRES. PRE-STRESSING OF THESE FIBERS IS PREFERABLY AFFECTED BY EMBODYING IN THE PHENOLIC BODY, PRIOR TO ITS CARBONIZATION PROCESS HAS ACRYLONITRILE WHOSE MORAML CARBONIZATION FIBRES MADE FROM BEEN COMDUCTED ONLY TO THE STARGE OF OXIDISING THE FIBERS WHILE THEY ARE UNDER SENSION. DURING THE SUBSEQUENT CARBONIZATION OF THE RESIN THE FIBRES WILL SHRINK MORE THAN THE RESIN, THEREBY PRODUCING PRE-STRESSING, OR ASSIING PREVIOUSLY MECHANICALLY APPLIED PRE-STRESSING, OF THE FIBERS IN THE RESULTING CARBON BODY.

en-"H160 K jeldUeD/D DR Patented Mar. 13, 1973 1 2 3 720 575 lieved tohave the particular advantage that bonding between the fibres and thematrix is more likely to occur gg g gg gg ggig E by pairing of theunpaired electrons created during the Frederick Clam] Cowlard Towcester,England, assign," firing, and 1S expected to result in a product ofparticularto Beckwith Carbon Corporation, Van Nuys, .Calif. y greatstrength capable of operating at temperatures In No Drawing. Filed Feb.3, 1971, Ser. No. 112,479 excess of 300 C. Claims priority, applicationGreat Britain, Feb. 6, 1970, 5,863/70, Int. Cl. B32b 16 EXAMPLE I Inorder to produce vitreous carbon reinforced with prestressed carbonfibres, a quantity of fibres made fromXB/ polyacrylonitrile, which havealready been subjected to h the initial stages of conversion into carbonfibres up to K US. Cl. 161-170 7 Claims ABSTRACT OF THE DISCLOSURE Amechanical strength of a carbon body made by carbonization of a phenolicresin body, which may be a solution of 40% formaldehyde. Excess of thesolution so-called vitreous carbon, is greatly increased by embodyispoured and a Solution of a novolak resin with a 5 7 mg thereinprestressed carbon fibres h h of phenol formaldehyde ratio of 1:1 isadded to cover the these fibres is preterahly ehecthdhy embodylhg 1n thelayer of carbon fibres. Additional layers of fibres are Phenolicbody'prior tolts carhohlzhhhnhbras made from positioned on top of thisfirst layer, and each of these acrylohitrhe whose normal h h h. processhas layers is covered with a layer of the same novolak resin. beenconducted only to the stage Of OXIdlSIIIg the fibres The tray is thenheated to a temperature of c. for whhe t Y are under h Dunne Shbsequent24 hours, during which time the fibres are allowed to carbhnlzatloh ofthe teem fibres Wlh .Shnhk h settle under the influence of gravity.Excess resin is then than the teeth thereby.produclhhrpreStressmh orassist poured off, leaving just sufficient resin to completely ingPheviously meehahleahy apph-ed pre'stresslhg of the 25 cover the fibrelayers. The resin is then cured by heating fibres 1n th resllhlng Carbony on a schedule to 160 for 7 days. If the fibres are randomly oriented,a loading of 40% is likely to be achieved, and if all fibres areoriented in the same direction, the This invention relates to themanufacture of carbon loading can be increased to approximately Thebodies reinforced by embedded carbon fibres. According fibre compositeis then heated above the normal curing to my coependihg t h tt Stemperature to a temperature of approximately 800 C. filed an- 1972Whlch 1S a eohhhuattohlh'part of at a rate sufficiently low to ensureconversion of the resin plication 5611 59,017, filed. July 2 how of thematrix to vitreous carbon. During this heating aban o a bonded h h body15 made, by process the conversion of the polyacrylonitrile fibres toranging earboh hhres m a math? of thermosethhg carbon fibres is alsocompleted and the oxidised fibre will thetic r s paftlcularlyphehol'aldehyde resm' shrink more than the resin, with the result thatthe fibre after heat-curing the resin in a customary manner, the is keptin tension in the finished matrix. heat treatment of the thermosettingresin is extended beyond its normal curing temperature to convert theEXAMPLE II synthetic resin into carbon material; the heat treatment 40In order to produce carbon material of even greater may be arranged toreach temperature of about strength, though somewhat inferior resistanceto heat .1800, at Whlch the formahoh of true Vmeous carbon and chemicalattack, the method of Example I is modified 1s eomphted, or It may becamehtonly t temperanire by limiting the further heating of thecomposite body Whlch though well above the eunhg point the h aftercompletion of the curing to a maximum temperature. may be well below thetemperature of 1800 h i which, while at least equal to the temperatureof about for the completion of eohversleh the syhthehc rehlh 1100 C.required for completing the conversion of the t0 Vitreous carbon and byihsertthg Into the hi texthe fibres into carbon fibre, is lower than thetemperature of Of other Synthetic fibree ht a P t cohchhoh a 1800 C. atwhich conversion of the resin of the matrix ihtorced earbeh body Inwhtch the remforclhg carbon into vitreous carbon would be completed, forexample fibres are prestressed for tension can be produced, probylimiting this further heating to a maximum tempera vided that the firingof the resin body is extended to a ture of 1150. C. 1 temperaturesufficient to convert the fibres to carbon fibres This will result inthe production of a largely can and that h material t the resinous body18 so chosen bonised matrix reinforced with carbon fibres which, due asto h' 1655 dhrlhg the he treatment than the to their greatercontraction, are under tension in the fi materlals matrix and thus inthe formation of a composite body The Present lhvehtloh prophsesgenerally to Provlde having a high transverse strength and high elasticdea carbon body reinforced with carbon fibres, whose f0rmabi]itystrength is increased by the fact that the fibres are put in EXAMPLESHLIV tension. Apart from the method just described this may be achievedby using partially carbonised fibres which in The methods of Example eExample 11 F P the case of fibres made from polyacrylonitrile, are takentlvely are medlhed by shbsttthtlhg for the quantity of after theoxidation stage, which is carried out while the 3 ahfahged fibres 51 y hf P r fibres fibres are under tension, loading them into a phenolic{mounted f under longltudmal tehslon and P resin and then firing thecomposite. This will ensure that mg t malfltalhlng h fibres thusthnsloned these during firing shrinkage of the fibres will be greaterthan 5 mechahlflal means dhnhg the Whole the Chung and that of thematrix, thus keeping the fibres under tension carhomslng Processes ofthe resin in the matrix. Alternatively or in addition the whole ofEXAMPLES the curing and carbonisation processes of the synthetic resinmay be carried out with the carbon fibres put in The methods of ExampleIII and Example IV are moditension by external means applying amechanical force. 7 fied by substituting aligned high-modulus carbonfibres The system of firing a composite product containing partiallycured carbon fibres in a resinous matrix is beand including the stageofoxidising the fibres while they are under tension, is laid-out in theform of a mat in a 2 tray coated with polypropylene sheet and is soakedwithX for the partly converted polyacrylonitrile fibres of Examples IIIand IV.

What we claim is:

1. A carbon body consisting of a carbon matrix which is reinforced bycarbon fibres which are embedded therein under tensile stress so thatthe material of the matrix is under compressive stress.

2. A method of making a carbon body reinforced with carbon fibres thatare under tensile stress, which comprises the steps of arranging fibresof organic material which have been subjected to oxidising heattreatment under tensile stress so as to be convertible by further heattreatment into carbon fibres under longitudinal shrinkage in a matrix ofthermosetting synthetic resin which, when subjected to such further heattratment, is subject to less shrinkage than the said fibres, curing theresin of the matrix, and subjecting the cured body to heat treatment toa temperature sufiicient to convert the fibres into carbon fibres.

3. A method as claimed in claim 2, wherein the fibres employed arefibres made from acrylonitrile which have already been subjected to theinitial stages of conversion to carbon fibres up to and including astage of oxidising the fibres while they are under tension but whichrequire further heating to be converted into carbon fibres.

4. A method as claimed in claim 2, which includes the step ofmechanically tensioning said fibres before curing the matrix andmaintaining the fibres under mechanically applied tension while thematrix is being cured and while the cured body is subjected to heattreatment to convert the fibres into carbon fibres.

5. A method of making a carbon body reinforced with carbon fibres thatare under tensile stress, which 4 comprises the steps of arranging, in amatrix of thermosetting synthetic resin, carbon fibres or fibres oforganic material which are convertible by heat treatment into carbonfibres, mechanically tensioning said fibres and curing the resin of thematrix while maintaining the fibres under mechanically applied tension,and subjecting the cured body to heat treatment to convert the curedbody into a carbon body reinforced by carbon fibres while maintainingthe fibres under mechanically applied tension. 6. A method as claimed inclaim 5, wherein aligned high-modulus carborLlibLqS are employed.

"Tfikmetlibi'isdlaimed in claim 5, wherein the fibres employed arefibres made from acrylonitrile which have already been subjected to theinitial stages of conversion to carbon fibres up to and including astage of oxidising the fibres while they are under tension but whichrequire further heating to be converted into carbon fibres.

References Cited UNITED STATES PATENTS 3,412,062 11/1968 Johnson et al.260-37 3,233,014 2/1966 Bickerdike et al. 26429 3,462,289 8/1969 Rohl eta1. 11746 3,576,769 4/1971 Hirsch 8--115.5 X

WILLIAM A. POWELL, Primary Examiner US. Cl. X.R.

